It's well known to ablate body tissue using a microwave applicator which heats and destroys the surrounding tissue. One use of such an applicator is in the non-invasive treatment of cancer in an internal body organ such as the liver. GB2415630 discloses an applicator of the above-mentioned type comprising a probe having a thin elongate shaft, which can be inserted into the patient. The proximal end of the probe comprises a handle which is connected to an external microwave generator by an elongate flexible cable. A thin elongate microwave transmission line extends inside the probe from the handle to a radiating tip disposed at or adjacent the distal end of the probe. In use, the microwave field radiated from the tip heats and ablates the surrounding tissue in a localised area.
A disadvantage of the above-mentioned applicator is that the probe can heat up for a variety of reasons. Firstly, power losses can occur in the transmission line extending along the probe to the tip, which power losses heat the transmission line and the surrounding parts of the probe. Secondly, the radiated microwave energy can heat the probe. Thirdly, the heat from the ablation can be conducted back along the probe. Such heating of the probe is undesirable, since it can burn the patient's skin at the point of entry of the probe or it can burn other parts of the patient's body adjacent the shaft of the probe. Indeed, UK government regulations specify that no external part of any medical apparatus should exceed 48° in temperature.
In order to overcome the above-mentioned problems, it is well known to pass a liquid, such as a saline solution, along the probe so as to cool the probe. In use, the liquid passes out of the apertures in the distal end of the probe into the surrounding body cavity. A disadvantage of this arrangement is that the liquid fills the wound and undesirably either flows out of or into the body. Furthermore, the radiated microwave energy can heat the liquid in the body cavity.
In order to overcome the above-mentioned problems, WO2005/011049, DE2407559 and U.S. Pat. No. 4,375,220 each disclose microwave applicators in which cooling fluid is passed along the probe to its distal end along one flow passage and then returned along another flow passage.
In order to achieve this, each of the above-mentioned applicators comprise a complicated arrangement of cooling pipes or formers inside the probe, which define the flow and return passages. It will be appreciated that microwave applicator probes are advantageously thin, in order to enable them to be used as non-invasively as possible. However, a disadvantage of the pipes and formers used in the above-mentioned applicators is that the flow and return passages need to be relatively large in order to achieve the desired flow rates and it will be appreciated that this correspondingly increases the overall diameter of the probe. Furthermore, the probe also needs to be of a relatively large diameter in order to facilitate the insertion of the pipes or former.
We have now devised a microwave applicator which alleviates the above-mentioned problems.